Is it Acrobat XI Pro or Standard? Only the former has this option built-in. You can still do it with the Standard version, but it will require using a script.
As try67 mentioned, redaction tool is available in Acrobat XI Pro. You may refer to the steps given in the following link to check the product installed on the machine: Identify the product and its version for Acrobat and Reader DC
You may also refer to the following forum threads discussing the similar topic:
Let us know if you have a further query.
I have Adobe XI Standard. I'll have my IT administrator install Adobe XI Pro so I can have the redact capability.
Thank you all for your answers!!